Lightning arrest assembly

ABSTRACT

Three lightning arresters including a characteristic element in series with gaps are disposed in individual parallel openings within a single insulating housing with their longitudinal axes located at apices of a regular triangle. The openings are closed at one end on the incoming-line side by the end portion of the housing through which three terminals are sealed to be connected to the respective arresters and in which one annular metallic shield is embedded so as to be connected to each terminal.

United States Patent Inventors Takayoshi Kamada;

Nobuo Nagal; Shojl Tada, all of Arnlgasaki,

Japan Appl. No. 80,042 Filed Oct. 12,1970 Patented Dec. 21, 1971 Assignee Mitsubishi Denlrl Kabushiki Kalsha Tokyo, Japan Priority Oct. 15, 1969 Japan 44/98079 LIGHTNING ARREST ASSEMBLY 4 Clalml, 10 Drawing l 'lgs.

U.S. Cl. 317/69, 317/68 Int. Cl 1102b 9/06 Fleld 01 Search 317/69, 68,

[56] References Cited UNITED STATES PATENTS 1,311,916 8/1919 Reid 317/69 2,507,363 5/1950 Baker 317/69 2,670,452 2/1954 Yonkers et al.... 317/69 X 3,513,354 5/1970 Sakshaug et al. 317/69 X Primary Examiner-James D. Trammell Attorneys-Robert E. Burns and Emmanuel .l. Lobato ABSTRACT: Three lightning arresters including a characteristic element in series with gaps are disposed in individual parallel openings within a single insulating housing with their longitudinal axes located at apices of a regular triangle. The openings are closed at one end on the incoming-line side by the end portion of the housing through which three terminals are sealed to be connected to the respective arresters and in which one annular metallic shield is embedded so as to be connected to each terminal.

LIGHTNING ARREST ASSEMBLY BACKGROUND OF THE INVENTION This invention relates to a lightning arrester assembly including a plurality of lightning arrester units disposed within a single housing of electrically insulating material.

There have been already known lightning arresters employing a lightning arrester unit consisting of one or more characteristic or valve elements disposed in series with insulating gaps within an electric insulation tube such as a porcelain tube. If it is desired to equip individual phases of an electric polyphase system with such lightning arresters disposed in juxtaposed relationship then each of the arresters is required to be spaced away from the adjacent arresters and, if present, a point of ground potential by at least minimum necessary distances required to prevent the gaps in the arrester from deteriorating in potential distribution due to the interaction of the potentials of the system phases and also to that point. This has resulted in the disadvantage that it is difficult to dispose the lightning arresters in a small space.

Also it has been previously practical to cover the outer wall surface of the above-mentioned insulation tube with an earthed sheath. The latter arresters have been able to be equipped in the closest packing relationship on an electric polyphase system because of the presence of their earthed sheaths. This has resulted in a decrease in space occupied by the arresters as compared with the first-mentioned arresters. However, when equipped in the closest packing relationship on a three-phase system, for example, the sheathed arresters have required a space for equipment equal to about three time the space for a single phase. Also the gaps in each arrester have been spaced away from the corresponding gaps in the adjacent arresters by distances equal to twice the wall thickness of the insulation tube, assuming that the earthed sheath is negligibly thin. On the other hand, the gaps in each arrester have a voltage-to-ground equal to ENS where E represents the line voltage of the system. Therefore a voltage across the corresponding gaps in the adjacent arresters is only increased by a factor of the square root of three (V?) as compared with the voltage-to-ground. Thus each of the sheathed arresters has been spaced away from the adjacent arresters by a distance larger than it need. This means that there is a possibility of further decreasing the distance between the adjacent arresters.

SUMMARY OF THE INVENTION Accordingly it is the chief object of the invention to provide a new and improved lightning arrester assembly decreased in dimension as compared with the prior art type lightning arrester assemblies.

It is another object of the invention to provide a new and improved lightning arrester assembly capable of being equipped on an electric system in simple manner.

It is still another object of the invention to save labors upon efi'ecting the maintenance and inspection of the lightning arresters.

The invention accomplishes these objects by the provision of a lightning arrester assembly comprising a plurality of lightning arresters having longitudinal axes disposed in sub stantially parallel relationship, and one terminal on the incoming line side connected to each of the arresters, characterized in that there is provided a single housing of electrically insulating material having disposed therein both the plurality of lightning arresters and one shield electrically connected to each of the terminals.

The housing may be preferably provided on that end portion thereof disposed on the incoming-line side with a step surrounding each of the terminals.

The housing may be advantageously provided on the outer peripheral wall surface thereof with a metallic coating connected to ground.

The housing may have conveniently a cover member detachably disposed on that end located on the ground side in common to the plurality of lightning arresters.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is an elevational view, partly in longitudinal section of one form of the prior art type lightning arresters;

FIG. 2 is a view similar to FIG. 1 but illustrating another form of the prior art type lightning arresters;

FIG. 3 is a diagrammatic elevational view illustrating the manner in which the lightning arresters shown in FIG. 1 are equipped on an electric three-phase system;

FIG. 4 is a fragmental elevational view of an assembly of the lightning arresters shown in FIG. 2 and closely packed for use in an electric three-phase system;

FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 4 and viewed in the direction of the arrows shown in the same FIGURE;

FIG. 6 is a graph plotting a ratio of the actual-to-theoretical value of a discharging voltage across a gap against a distance between the gap and a charged body for the conventional lightning arrester shown in FIG. 1;

FIG. 7 is a plan view of one embodiment constructed in accordance of the lightning arrester assembly-of the invention;

FIG. 8 is a fragmental longitudinal sectional view taken along the line of VIII-VIII of FIG. 8 and viewed in the direction of the arrows shown in the same FIGURE;

FIG. 9 is a plan view of a modification of the invention; and

FIG. 10 is a fragmental longitudinal view taken along the line of XX of FIG. 9 and viewed in the direction of the arrows shown in the same FIGURE.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and FIG. 1 in particular, it is seen that a lightning arrester generally designated by the reference numeral 10 comprises an insulation tube 12 such as a porcelain tube and a lightning arrester unit including an insulating gap member 14 forming gaps and a pair of characteristic or valve elements 16 disposed in series circuit relationship within the tube 12. Disposed upon one side of the arrester element, in this case, upon the gap member 14 is a contact spring 18 for purpose of electrical connection. A pair of metallic covers 20 close both ends of the insulation tube 12 and cooperate with individual O-rings 22 interposed between the same and the end faces of the tube 12 to maintain the interior of the tube 12 hermetic with the tubes interior filled with an amount of any suitable gas 24 in its dried state. The lower characteristic element 16 abuts against the lower cover 20. Then one metallic terminal 26 is connected to each of the upper and lower covers 20.

FIG. 2 shows another lightning arrester of the conventional construction suitable for use in an electric substation intended to be small-sized such as a miniature substation. A cylindrical housing 12 formed on any suitable electrically insulating material such as epoxy resin has disposed therein a lightning arrester unit including a gap member 14, a contact spring 18, and a pair of characteristic elements 16 interconnected in series circuit relationship in the named order.

The gap member 14 is connected to a metallic terminal 24 sealed through the closed end of the housing 12 while the lower characteristic element 16 abuts against a metallic cover 20 serving to close the other or open end of the housing 12. The cover 20 is fixedly secured to the open end face of the housing 12 by having bolts 28 extending therethrough and screw-threaded into the respective female screws 30 embedded in the apertured end portion of the housing. Then an O-ring 22 is interposed between the metallic cover 20 and the apertured end face of the housing 12 to maintain the interior of the housing hermetic. As in the arrangement of FIG. 1, an

amount of any suitable gas 24 in its dried state is sealed in the.

interior of the housing 12.

The arrangement is much different from that shown in FIG. I in that in FIG. 2 a metallic sheath or coating 32 is disposed on the outer peripheral wall surface of the insulating housing 12 to be connected to the metallic cover 20. That is the coating 32 and the cover 26 are maintained at the same potential or ground potential during service.

A plurality of the lightning arresters as shown in FIG. 1 can be equipped in juxtaposed relationship on an electric polyphase system. FIG. 3 shows by way of example, three lightning arresters l equipped on an electric three-phase system. The three arresters are disposed in aligned spacedrelationship and have the upper terminals 26 connected to the respective lines or phase of the electric system through leads 34 while the lower terminals 26 are connected to ground through leads 36 respectively.

With a plurality of lightning arresters put side by side as shown in FIG. 3, there is a fear that the potentials on the respective system phases will be interacted to deteriorate a voltage distribution along each gap in the arresters. Therefore the arresters are required to be spaced away from one another by minimum necessary distances required to avoid that fear. Those distances are shown in FIG. 3 as being of 0. Similarly if a point of ground potential is located in the vicinity of any one of the arresters, a minimum necessary distance should be maintained therebetween for the same reason as abovedescribed. This is illustrated in FIG. 3 by one hatched portion 38 spaced away from each of the outer arresters 10 by a minimum necessary distance of b with the hatched portions designating earthed structures. It will readily be understood that any one of the lightning arresters is effectively prevented from flashing over the gap therein as far as that arrester is spaced away from the adjacent arrester or point of ground potential by the distances of a or b or more.

Upon equipping lightning arresters on an electric system it is necessary to consider a ratio of the actual-to-theoretical value of a discharge voltage across a gap involved which is plotted in FIG. 6 against a distance between the gap and on a charged body such as another gap or an earthed structure for the arrester shown in FIG. 1. In FIG. 6 the axis of ordinates represents the ratio just described in percent and the axis of abscissas represents the distance in an arbitary unit. Curve a depicts the relationship between a gap and a charged body or another gap and curve [2 depicts that between a gap and an earthed structure with the reference character 1" denoting a minimum necessary distance required to maintain the insulation between the gap and earthed member.

From FIG. 6 it will be appreciated that it is difficult to gain the ratio as above described approximating 100 percent unless the particular gap is spaced away from ground or the adjacent charged body by a distance exceeding a minimum necessary distance required to insulate the two from each other. This results in the necessity of equipping the arresters on the associated electric system while each of the arresters is maintained spaced away from the adjacent arresters by distances larger than its insulation distance. Therefore it is difficult to dispose the arresters in a small space for equipment.

On the other hand, lightning arresters such as shown in FIG. 4 include the earthed sheath and therefor do not require so large space for equipment as those illustrated in FIG. 1 because they are disposed in the closest packing relationship. For example, a triad of the sheathed arresters can be closely packed into a regular triangle-shaped cross section and equipped on a three-phase system as best shown in FIG. 5. In that event, as shown in FIG. 4, the terminal 26 of each arrester I0 is connected to each line of the three-phase system (not shown) through a conductor 40 embedded in a cylindrical insulation 42 substantially equal to the arrester 10. However because of the presence of the earthed sheath, the three arresters require a space for the equipment thereof equal to about three times the space for a single-phase system and dif ficult to decrease below the figure just specified.

The sheathed arrester 10 is shown in FIG. 5 as including the insulating housing 12 having a wall thickness of c which, in turn, provides an insulation distance between one gap member and the earthed sheath 32. With the three arresters l0 closely paced as best shown in FIG. 5, a spacing d between the gap in each arrester and the corresponding gap in the adjacent arresters is equal to twice the insulation distance of 0 because the sheaths are negligibly thin.

On the other hand, the arresters connected to a three-phase system each are at a voltage-to-ground equal to E/Viwhere E represents the line voltage thereof. Thus a voltage between the gap members in the adjacent arresters is only higher than the voltage-to-ground by a factor of the square root of three (V5). This means that any pair of the sheathed arresters are spaced away from each other by a distance larger than they need. In other words, there is possibility for further decreasing the radial dimension of the arrester.

The invention contemplates to decrease the overall dimension of an assembly including a plurality of lightning arresters. Referring now to FIGS. 7 and 8 wherein like reference numerals designate the components corresponding or similar to those shown in FIGS. 1 and 2, there is shown one form of the invention applied to a three-phase system. The arrangement illustrated comprises a housing 12 formed of any suitable, electrically insulating material such as epoxy resin and including three openings 50 longitudinally extending in substantially parallel relationship therethrough with one end thereof in this example the upper ends thereof as viewed in FIG. 8 closed. The longitudinal axes of the openings 50 are located at the apices of a regular triangle. Disposed within each of the openings 50 is a lightning arrester unit including a gap member 14 forming a plurality of series gaps, a pair of characteristic elements 16 and a contact spring 18 connected in series circuit relationship in the named order as in the arrangement shown in FIG. 1 or 2. If desired, any desired number of the characteristic elements may be used.

The housing 12 has a common cover 26 closing the open ends or the lower ends as viewed in FIG. 7 of all the openings 50. The cover 26 is adapted to be connected to ground. A plurality of bolts 28 extend through the cover 26 and are screwthreaded into the respective female screws 30 (one of which is illustrated in FIG. 8) embedded in the lower end faces of the housing 12. Then one O-ring 22 is interposed between the cover 26 and the lower end face of the housing 12 around each opening 50 and cooperates with the common cover 26 to hermetically seal the openings 50 filled with any suitable gas in its dried state as in the arrangement shown in FIG. I or 2.

That portion of the housing 12 closing each of the openings 50 is in the form of a truncated cone having disposed on the outer periphery an annular step 52 serving to provide the necessary creeping distance required for across the respective phases of the associated electric system in the atmosphere. If desired, two or more steps may be used. One metallic terminal 26 on the incoming-line side seals through each of the tapered, stepped end portions of the housing 12 until it engages the associated gap member I4 disposed within each opening 50.

As shown in FIG. 8, an annular shield generally designated by the reference numeral 54 is embedded in the housing 12 adjacent the closed end of the opening 50 to be connected to the terminal 26. The shield 54 is formed of a metallic annulus 54-1 having an outer peripheral portion bent toward the as' sociated gap member 14 and a metallic ring 54-2 attached to the outer edge thereof with the annulus 54-] connected to the terminal 26. It is to be understood that an annular shield identical to the shield 54 should be operative coupled to each of the remaining gap members although such shields are not illustrated.

FIGS. 9 and 10 show an arrangement substantially identical to that illustrated in FIGS. 8 and 9 expecting that the housing 12 includes a flat end portion for closing the openings 50 and that an earthed shield or coating 32 is disposed on the outer peripheral wall surface of the housing 12 to be connected to the cover 20 as in the arrangement of FIG. 2.

In summary, the invention provides a lightning arrester assembly comprising a plurality of lightning arrester units disposed in spaced parallel relationship within a single insulting housing and one annular shield embedded in the housing adjacent each of the arrester units to be connected to the associated terminal on the incomingline side.

Therefore, if lightning strikes any phase of an electric system embodying the principles of the invention, the annular shields are effective for maintaining the discharge voltage across each gap unchanged regardless of whether or not the housing includes the earthed sheath. Thus it is not required to render a distance for interphase insulation large. For threephase systems, it is sufiicient to render the distance for interphase insulation equal to the insulation distance ground multiplied by a factor of the square root of three or\/ 3 In general, a ratio of the insulation distance-to-ground to the distance for interphase insulation is proportional to a ratio of a voltage-to-ground to a line voltage of the particular electric system.

Further, it will be appreciated that, due to the presence of the annular shields, the lightning arrester units are permitted to be more close to one another than those shown in H08. 4 and 5 with no change in discharge voltage across each gap. Therefore the lightning arrester assembly decreases in the overall dimension. In addition, as a plurality of lightning arrester units are disposed in a single insulating housing the resulting assembly can be very easily equipped on the particular electric system and subject to maintenance and inspection with labors saved. in the arrangement as shown in FIGS. 7 and 8, the step 52 is disposed on each of those portions of the housing enclosing the terminals on the incoming-line side to permit the arrester units to be sufficiently insulated from one another for the particular line voltage as well as preventing a decrease in interphase insulation due to contaminations on such portions of the housing. Therefore the assembly can further decrease in the overall dimension. Where the arrester assembly has been small-sized as above described, it is possible to dispose the assembly in a small space in which the conventional arrester assembly could not be mounted with the result that it can be realized to expand a range of an electric system to be protected and render installations of electric substations small-sized.

While the invention has been illustrated and described in conjunction with a few preferred embodiments thereof it is to be understood that various changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention. For example, the annular shield may be formed of a plurality of L-shaped rods radially extending from the associated terminal and preferably at equal angular intervals such as spokes and a ring attached to the free bent ends of the rods with satisfactory results. Also the invention is equally applicable to electric systems including any desired number of phases. In the latter event, a plurality of lightning arrester units equal in the number to the phases are disposed within a single insulating housing in spaced parallel relationship and preferably symmetrically with respect to the longitudinal axis of the housing at equal angular intervals.

What we claim is:

1. A lightning arrester assembly comprising a plurality of lightning arresters having longitudinal axes disposed in substantially parallel relationship, a single housing of electrically insulating material having disposed therein said plurality of lightning arresters, one terminal in the incoming-line side electrically connected to each of said lightning arresters, and one shield disposed in said insulating housing to be electrically connected to each of said terminals.

2. A lightning arrester assembly as claimed in claim 1 wherein said insulating housing is provided on that end portion thereof disposed on the incoming-line side with a step surrounding each of said terminals.

3. A lightning arrester assembly as claimed in claim 1 wherein said insulating housing is provided on the outer peripheral wall surface with a metallic coating electrically connected to ground.

4. A lightning arrester assembly as claimed in claim 1 wherein said insulating housing is provided on that end portion thereof disposed on the earthed side with a detachable cover common to all said lightning arresters. 

1. A lightning arrester assembly comprising a plurality of lightning arresters having longitudinal axes disposed in substantially parallel relationship, a single housing of electrically insulating material having disposed therein said plurality of lightning arresters, one terminal in the incomingline side electrically connected to each of said lightning arresters, and one shield disposed in said insulating housing to be electrically connected to each of said terminals.
 2. A lightning arrester assembly as claimed in claim 1 wherein said insulating housing is provided on that end portion thereof disposed on the incoming-line side with a step surrounding each of said terminals.
 3. A lightning arrester assembly as claimed in claim 1 wherein said insulating housing is provided on the outer peripheral wall surface with a metallic coating electrically connected to ground.
 4. A lightning arrester assembly as claimed in claim 1 wherein said insulating housing is provided on that end portion thereof disposed on the earthed side with a detachable cover common to all said lightning arresters. 